Effects of ghost dark energy perturbations on the evolution of spherical overdensities

Abstract

While in the standard cosmological model the accelerated expansion of the Universe is explained by invoking the presence of the cosmological constant term, it is still unclear the true origin of this stunning observational fact. It is therefore interesting to explore alternatives to the simplest scenario, in particular by assuming a more general framework where the fluid responsible of the accelerated expansion is characterised by a time-dependant equation of state. Usually these models, dubbed dark energy models, are purely phenomenological, but in this work we concentrate on a theoretically justified model, the ghost dark energy model. Within the framework of the spherical collapse model, we evaluate effects of dark energy perturbations both at the linear and non-linear level and transfer these results into an observable quantity, the mass function, by speculatively taking into account contributions of dark energy to the mass of the halos. We showed that the growth rate is higher in ghost models and that perturbations enhance the number of structures with respect to the ΛCDM model, with stronger effects when the total mass takes into account dark energy clumps.

Structure formation in clustering DBI dark energy model with constant sound speed

“…The figures show that (i) for the case of FCL (c eff = 0), DBI perturbations clearly make δ c closer to the ΛCDM compared to the corresponding non-clustering DBI models. This is in well agreement with what found by Pace et al (2010); Batista & Pace (2013); Pace et al (2014b); Malekjani et al (2015). (ii) At high redshifts, the linear overdensity tends to the fiducial value δ c = 1.686 in the EdS Universe.…”

“…Note that Pace et al (2017) have shown that the tendency of δ c to the EdS limit at early times strongly depends on the value of the numerical infinity δ ∞ and on the choice of the initial time to start the integration of the equations, a i . In our numerical calculations to satisfy the EdS limit, follow- Malekjani et al (2015). (v) At high redshift, the values of overdensity at turn-around epoch ζ for DBI model asymptotically tends to the value in the EdS Universe ζ = 5.55.…”

Model selection and constraints from holographic dark energy scenarios

“…We focus our analysis at sub-horizon scales, where the results of Pseudo Newtonian dynamics are well consistent with those of General Relativity (GR) paradigm (see Abramo et al 2007). In this context, two different scenarios have been studied in literature (Armendariz-Picon et al 1999;Garriga & Mukhanov 1999;Armendariz-Picon et al 2000;Erickson et al 2002;Bean & Doré 2004;Hu & Scranton 2004;Abramo et al 2007Abramo et al , 2008Bean & Doré Bal;Abramo et al 2009;Basilakos et al 2009a;de Putter et al 2010;Pace et al 2010;Akhoury et al 2011;Sapone & Majerotto 2012;Pace et al 2012;Batista & Pace 2013;Dossett & Ishak 2013;Batista 2014;Basse et al 2014;Pace et al 2014b,a,c;Malekjani et al 2015;Naderi et al 2015;Mehrabi et al 2015a,b,c;Nazari-Pooya et al 2016;Malekjani et al 2017). In the first scenario the DE component is homogeneous and only the corresponding non-relativistic matter is allowed to clump, while in the second scenario the whole system clusters (both matter and DE).…”

Agegraphic dark energy: growth index and cosmological implications

“…In other words DE acts against gravity which implies that more suppression of the growth of matter perturbations is taking place. While, if DE is allowed to clump in a similar manner to dark matter then the total energy of DE can not act against the force of gravity (see also Malekjani et al 2015).…”